As is well known, a Gilbert switch pair produces a differential output signal that is proportional to two input signals. These switches are often used for frequency conversion in, for example, a radio system, as they provide an output current that is an accurate multiplication of the differential base currents of the two input signals. Further, as used in a mixer, this balanced operation cancels out many unwanted mixing products and provides a more accurate output.
In many applications, it is desirable to increase the conversion gain of the active mixer. In one known approach, the overall current of the mixer and the LO (Local Oscillator) drive are increased. This approach, however, can make it more difficult for the switches to switch and may have to increase the current quite a bit. An increase in the LO swing, which can switch the Gilbert switch harder, increases the gain but at the cost of increased DC power consumption which is an undesirable side effect.
What is needed, however, is a better approach to improving the gain and, therefore, the sensitivity of a Gilbert switch.